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In my script I am comparing the temp variable and if it is blank I want to update the temp variable. But the below script is not working.

Script:

temp=`head -5 $filename1 | tail -1` if [ "$temp" == " " ] then temp=`head -6 $filename1 | tail -1` echo "Blank - Updated temp value" else echo "$temp not blank" fi

Upon troubleshooting I found this when I used the od command. When I checked the temp variable it has special characters because of that its not considering it has blank.

echo $temp | od -c 0000000 \r \n 0000002

Can you help on how to ignore the above special characters?

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  • 1
    To strip the carriage return and newline from the output, you might temp=$(head -5 $filename | tail -1 | tr -d '\r\n') Commented Mar 8, 2017 at 19:10
  • 1
    Pre-process with dos2unix to fix that and potentially other idiosyncrasies of Microsoft text formats. Commented Mar 8, 2017 at 22:13

2 Answers 2

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First things first:

if [ "$temp" == " " ]

The comparison operator is actually =, not ==. The latter works in some shells, but isn't standard. Also, you're comparing the variable not against an empty string, but one containing a single space, which may or may not be what your file has.

If the file can contain extra whitespace, it might be a good idea to just remove all of it with sed or tr. And then you can just use [ -z "$temp" ] to test if it's empty. So:

temp=$(head -5 $filename | tail -1 | tr -d ' \t\r') if [ -z "$temp" ] ; then ...

Instead of head and tail, you can use sed to pick a single line:

temp=$(sed -n '5p' | tr -d ' \t\r') if [ -z "$temp" ] ; then ...

(5p means "on line 5, (p)rint the line", and -n inhibits the default action of printing any lines.)

Actually, instead of the test I'm a bit tempted to just go through the file with an awk script to get the fifth or sixth line depending on if the fifth has anything:

temp=$(tr -d ' \t\r' < $filename1 | awk '(NR==5 && $0) || NR==6 {print; exit}' )

(NR==5 tests the current line (record) number, $0 expands to the contents of the line, and is "true" if the line is not empty, && and || are the usual and and or operations)

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Using sed and removing all whitespace characters... temp=$(head -5 $filename1 | tail -1 | sed -r 's/\s+//g')

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